1. Field of the Invention
The present invention relates to a medium conveying mechanism in an image equipment such as a printer or a scanner, and more particularly, to a de-skew mechanism.
2. Description of the Prior Art
Sometimes images are printed or scanned to be oblique due to skew of the medium or tolerances of the roller assembly. To avoid the above condition, various methods are utilized to de-skew before the medium enters the printing or scanning area.
U.S. Pat. No. 6,011,948 discloses a correcting device in an image formation equipment. Please refer to FIG. 10, 11. The correcting device includes shutter members 15 and a connecting member 16. The shutter members 15 are integrally connected to one another via the connecting member 16. The correcting device is engaged in a rotating manner with the rotary shaft 18, to which the free conveyer rollers 13 are fixed. The twisted coil spring 24 is engaged in a sliding manner with a rotary shaft 18 with the end 24b thereof on the side of the connecting member 16. The shutter members 15 are provided with the collision surfaces 20a, which act as sheet leading edge collision surfaces. The sheet S forms a curved loop when pushing the shutter members 15, and after the shutter members 15 turn a certain angle, skew of the sheet S is corrected. After sheet S passes through the roller group, the shutter members 15 return to their initial positions by the twisted coil spring 24. The correcting device has a simple structure and lower cost, but it has some disadvantages. For example, when the sheet S passes through the roller group, the shutter members 15 will exert greater force onto the sheet S by the twisted coil spring 24, and this tends to damage sheet S. In addition, the skew generated by the tolerance of roller assembly cannot be corrected by the correcting device since the correcting device is disposed on the rotary shaft 18. Furthermore, when the leading edge of the sheet S contacts the shutter members 15, the correcting process for the skew is performed while conveying the sheet S, which has counterproductive effects on the correction effort.